<header>
  <div class="btn_menu" id="btn_menu">
    <div class="line"></div>
    <div class="line"></div>
    <div class="line"></div>
  </div>
  <h2>back stage</h2>
  <div class="portrait">
    <a href="index.html" class="center_tab"></a>
  </div>
</header>